1. Field of the Invention
The present invention relates generally to a sheet conveying apparatus for a printer, and more particularly to a sheet conveying apparatus comprising rollers for conveying various types of sheets to a printing unit and exhaust ports, and a sheet exhaust guide for selecting one of the exhaust ports in accordance with the thickness of the sheet.
2. Description of the Related Art
When printing is effected on a continuous sheet (e.g. a fanfold sheet) and a non-continuous sheet (a thin sheet of "B5" size or the like, or a relatively thick and hard sheet such as a postcard) with use of a single printer, the following problems occur:
(1) In order to ensure the exact feeding of sheets, it is necessary that the contact state of a pair of driven and driving rollers on the upstream side of a printing unit and the contact state of a pair of driven and driving rollers on the downstream side of the printing unit be adjusted in accordance with the type of sheets.
For example, when a thin non-continuous sheet is subjected to printing, it is necessary that both driven rollers on the upstream and downstream sides of the printing unit be brought into contact with the associated driving rollers with a predetermined contact force. However, when a thick non-continuous sheet is subjected to printing, this contact force needs to be slightly weakened.
In the prior art, the contact state of the upstream-side rollers and the contact state of the downstream-side rollers have been adjusted independently, resulting in complex structure of the apparatus.
(2) In order for an operator to easily take out a printed sheet from an exhaust port, it is desirable that the exhaust port is provided in the uppe part of the printer. However, in the conventional apparatus, a printed sheet is often inverted while it is conveyed to the exhaust port; therefore, wrinkles may appear on a relatively thick and hard sheet such as a postcard. For this reason, the printer has upper and lower exhaust ports. In this case, the operator operates an exhaust guide according to the type of sheet, thus selecting one of the exhaust ports. However, the operator often forgets to select the exhaust port, and a trouble of exhaust of sheets may occur.